Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)

Levermann, Anders; Winkelmann, Ricarda; Albrecht, Torsten; Goelzer, Heiko; Golledge, Nicholas R.; Greve, Ralf; Huybrechts, Philippe; Jordan, Jim; Leguy, Gunter; Martin, Daniel; Morlighem, Mathieu; Pattyn, Frank; Pollard, David; Quiquet, Aurelien; Rodehacke, Christian; Seroussi, Helene; Sutter, Johannes; Zhang, Tong; Breedam, Jonas Van; Calov, Reinhard; DeConto, Robert; Dumas, Christophe; Garbe, Julius; Gudmundsson, G. Hilmar; Hoffman, Matthew J.; Humbert, Angelika; Kleiner, Thomas; Lipscomb, William H.; Meinshausen, Malte; Ng, Esmond; J., Sophie M.; Perego, Mauro; Price, Stephen F.; Saito, Fuyuki; Schlegel, Nicole-Jeanne; Sun, Sainan; W., Roderik S.

doi:10.5194/esd-11-35-2020

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Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)

Anders Levermann

, Ricarda Winkelmann

, Torsten Albrecht

, Heiko Goelzer, Nicholas R. Golledge

, Ralf Greve

, Philippe Huybrechts

, Jim Jordan

, Gunter Leguy

, Daniel Martin

, Mathieu Morlighem

, Frank Pattyn

, David Pollard, Aurelien Quiquet

, Christian Rodehacke

, Helene Seroussi

, Johannes Sutter

, Tong Zhang, Jonas Van Breedam

, Reinhard Calov, Robert DeConto, Christophe Dumas, Julius Garbe

, G. Hilmar Gudmundsson

, Matthew J. Hoffman

, Angelika Humbert

, Thomas Kleiner

, William H. Lipscomb, Malte Meinshausen

, Esmond Ng, Sophie M. J. Nowicki

, Mauro Perego, Stephen F. Price

, Fuyuki Saito

, Nicole-Jeanne Schlegel

, Sainan Sun

, Roderik S. W. van de Wal

Earth System Dynamics, Volume: 11, Issue: 1, Pages: 35 - 76

Swansea University Author: Jim Jordan

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DOI (Published version): 10.5194/esd-11-35-2020

Abstract

The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st...

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Published in:	Earth System Dynamics
ISSN:	2190-4987
Published:	Copernicus GmbH 2020
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URI:	https://cronfa.swan.ac.uk/Record/cronfa64530
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Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm. For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 ∘C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade.</abstract><type>Journal Article</type><journal>Earth System Dynamics</journal><volume>11</volume><journalNumber>1</journalNumber><paginationStart>35</paginationStart><paginationEnd>76</paginationEnd><publisher>Copernicus GmbH</publisher><placeOfPublication/><isbnPrint/><isbnElectronic/><issnPrint/><issnElectronic>2190-4987</issnElectronic><keywords>Sea level rise, Antarctica, Antarctic ice sheet, basal ice shelf, ice sheet models</keywords><publishedDay>14</publishedDay><publishedMonth>2</publishedMonth><publishedYear>2020</publishedYear><publishedDate>2020-02-14</publishedDate><doi>10.5194/esd-11-35-2020</doi><url>http://dx.doi.org/10.5194/esd-11-35-2020</url><notes/><college>COLLEGE NANME</college><department>Geography</department><CollegeCode>COLLEGE CODE</CollegeCode><DepartmentCode>SGE</DepartmentCode><institution>Swansea University</institution><apcterm/><funders>Support for Daniel Martin, Tong Zhang, Matthew J. Hoffman, Mauro Perego, Stephen F. Price, and Esmond Ng was provided through the Scientific Discovery through Advanced Computing (SciDAC) programme funded by the US Department of Energy (DOE), Office of Science, Biological and Environmental Research, and Advanced Scientific Computing Research programmes. Their contributions relied on computing resources from the National Energy Research Scientific Computing Center, a DOE Office of Science user facility supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231. Christian Rodehacke has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement 610055 as part of the Ice2Ice project. Heiko Goelzer has received funding from the programme of the Netherlands Earth System Science Centre (NESSC), financially supported by the Dutch Ministry of Education, Culture and Science (OCW) under grant no. 024.002.001. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Helene Seroussi and Nicole-Jeanne Schlegel were supported by grants from the NASA Cryospheric Science, Sea Level Change Team, and Modeling Analysis and Prediction programmes. Ralf Greve was supported by the Japan Society for the Promotion of Science (JSPS) under KAKENHI grant nos. JP16H02224, JP17H06104, and JP17H06323. The work of Thomas Kleiner and Angelika Humbert has been conducted in the framework of the PalMod project (FKZ: 01LP1511B), supported by the German Federal Ministry of Education and Research (BMBF) as a Research for Sustainability initiative (FONA). The material provided for the CISM model is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under cooperative agreement no. 1852977. Computing and data storage resources, including the Cheyenne supercomputer (https://www2.cisl.ucar.edu/resources/computational-systems/cheyenne, last access: 6 January 2020), were provided by the Computational and Information Systems Laboratory (CISL) at NCAR. Torsten Albrecht was supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme “Antarctic Research with comparative investigations in Arctic ice areas” by grants LE1448/6-1 and LE1448/7-1. Julius Garbe acknowledges funding from the Leibniz Association (project DominoES). Jonas Van Breedam and Philippe Huybrechts acknowledge support from the iceMOD project funded by the Research Foundation – Flanders (FWO-Vlaanderen). Malte Meinshausen received funding from the National Science Foundation (NSF grant no. 1739031) through the PROPHET project, a component of the International Thwaites Glacier Collaboration (ITGC).</funders><projectreference/><lastEdited>2023-10-04T12:00:00.0694534</lastEdited><Created>2023-09-13T13:20:57.0247292</Created><path><level id="1">Faculty of Science and Engineering</level><level id="2">School of Biosciences, Geography and Physics - Geography</level></path><authors><author><firstname>Anders</firstname><surname>Levermann</surname><orcid>0000-0003-4432-4704</orcid><order>1</order></author><author><firstname>Ricarda</firstname><surname>Winkelmann</surname><orcid>0000-0003-1248-3217</orcid><order>2</order></author><author><firstname>Torsten</firstname><surname>Albrecht</surname><orcid>0000-0001-7459-2860</orcid><order>3</order></author><author><firstname>Heiko</firstname><surname>Goelzer</surname><order>4</order></author><author><firstname>Nicholas R.</firstname><surname>Golledge</surname><orcid>0000-0001-7676-8970</orcid><order>5</order></author><author><firstname>Ralf</firstname><surname>Greve</surname><orcid>0000-0002-1341-4777</orcid><order>6</order></author><author><firstname>Philippe</firstname><surname>Huybrechts</surname><orcid>0000-0003-1406-0525</orcid><order>7</order></author><author><firstname>Jim</firstname><surname>Jordan</surname><orcid>0000-0001-8117-1976</orcid><order>8</order></author><author><firstname>Gunter</firstname><surname>Leguy</surname><orcid>0000-0002-9963-8076</orcid><order>9</order></author><author><firstname>Daniel</firstname><surname>Martin</surname><orcid>0000-0003-4488-2538</orcid><order>10</order></author><author><firstname>Mathieu</firstname><surname>Morlighem</surname><orcid>0000-0001-5219-1310</orcid><order>11</order></author><author><firstname>Frank</firstname><surname>Pattyn</surname><orcid>0000-0003-4805-5636</orcid><order>12</order></author><author><firstname>David</firstname><surname>Pollard</surname><order>13</order></author><author><firstname>Aurelien</firstname><surname>Quiquet</surname><orcid>0000-0001-6207-3043</orcid><order>14</order></author><author><firstname>Christian</firstname><surname>Rodehacke</surname><orcid>0000-0003-3110-3857</orcid><order>15</order></author><author><firstname>Helene</firstname><surname>Seroussi</surname><orcid>0000-0001-9201-1644</orcid><order>16</order></author><author><firstname>Johannes</firstname><surname>Sutter</surname><orcid>0000-0002-3357-2633</orcid><order>17</order></author><author><firstname>Tong</firstname><surname>Zhang</surname><order>18</order></author><author><firstname>Jonas Van</firstname><surname>Breedam</surname><orcid>0000-0003-1504-9520</orcid><order>19</order></author><author><firstname>Reinhard</firstname><surname>Calov</surname><order>20</order></author><author><firstname>Robert</firstname><surname>DeConto</surname><order>21</order></author><author><firstname>Christophe</firstname><surname>Dumas</surname><order>22</order></author><author><firstname>Julius</firstname><surname>Garbe</surname><orcid>0000-0003-3140-3307</orcid><order>23</order></author><author><firstname>G. Hilmar</firstname><surname>Gudmundsson</surname><orcid>0000-0003-4236-5369</orcid><order>24</order></author><author><firstname>Matthew J.</firstname><surname>Hoffman</surname><orcid>0000-0001-5076-0540</orcid><order>25</order></author><author><firstname>Angelika</firstname><surname>Humbert</surname><orcid>0000-0002-0244-8760</orcid><order>26</order></author><author><firstname>Thomas</firstname><surname>Kleiner</surname><orcid>0000-0001-7825-5765</orcid><order>27</order></author><author><firstname>William H.</firstname><surname>Lipscomb</surname><order>28</order></author><author><firstname>Malte</firstname><surname>Meinshausen</surname><orcid>0000-0003-4048-3521</orcid><order>29</order></author><author><firstname>Esmond</firstname><surname>Ng</surname><order>30</order></author><author><firstname>Sophie M. 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spelling	v2 64530 2023-09-13 Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2) 6f28f48bfe39cb898ba51e3114889cbe 0000-0001-8117-1976 Jim Jordan Jim Jordan true false 2023-09-13 SGE The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm. For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 ∘C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade. Journal Article Earth System Dynamics 11 1 35 76 Copernicus GmbH 2190-4987 Sea level rise, Antarctica, Antarctic ice sheet, basal ice shelf, ice sheet models 14 2 2020 2020-02-14 10.5194/esd-11-35-2020 http://dx.doi.org/10.5194/esd-11-35-2020 COLLEGE NANME Geography COLLEGE CODE SGE Swansea University Support for Daniel Martin, Tong Zhang, Matthew J. Hoffman, Mauro Perego, Stephen F. Price, and Esmond Ng was provided through the Scientific Discovery through Advanced Computing (SciDAC) programme funded by the US Department of Energy (DOE), Office of Science, Biological and Environmental Research, and Advanced Scientific Computing Research programmes. Their contributions relied on computing resources from the National Energy Research Scientific Computing Center, a DOE Office of Science user facility supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231. Christian Rodehacke has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement 610055 as part of the Ice2Ice project. Heiko Goelzer has received funding from the programme of the Netherlands Earth System Science Centre (NESSC), financially supported by the Dutch Ministry of Education, Culture and Science (OCW) under grant no. 024.002.001. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Helene Seroussi and Nicole-Jeanne Schlegel were supported by grants from the NASA Cryospheric Science, Sea Level Change Team, and Modeling Analysis and Prediction programmes. Ralf Greve was supported by the Japan Society for the Promotion of Science (JSPS) under KAKENHI grant nos. JP16H02224, JP17H06104, and JP17H06323. The work of Thomas Kleiner and Angelika Humbert has been conducted in the framework of the PalMod project (FKZ: 01LP1511B), supported by the German Federal Ministry of Education and Research (BMBF) as a Research for Sustainability initiative (FONA). The material provided for the CISM model is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under cooperative agreement no. 1852977. Computing and data storage resources, including the Cheyenne supercomputer (https://www2.cisl.ucar.edu/resources/computational-systems/cheyenne, last access: 6 January 2020), were provided by the Computational and Information Systems Laboratory (CISL) at NCAR. Torsten Albrecht was supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme “Antarctic Research with comparative investigations in Arctic ice areas” by grants LE1448/6-1 and LE1448/7-1. Julius Garbe acknowledges funding from the Leibniz Association (project DominoES). Jonas Van Breedam and Philippe Huybrechts acknowledge support from the iceMOD project funded by the Research Foundation – Flanders (FWO-Vlaanderen). Malte Meinshausen received funding from the National Science Foundation (NSF grant no. 1739031) through the PROPHET project, a component of the International Thwaites Glacier Collaboration (ITGC). 2023-10-04T12:00:00.0694534 2023-09-13T13:20:57.0247292 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Geography Anders Levermann 0000-0003-4432-4704 1 Ricarda Winkelmann 0000-0003-1248-3217 2 Torsten Albrecht 0000-0001-7459-2860 3 Heiko Goelzer 4 Nicholas R. Golledge 0000-0001-7676-8970 5 Ralf Greve 0000-0002-1341-4777 6 Philippe Huybrechts 0000-0003-1406-0525 7 Jim Jordan 0000-0001-8117-1976 8 Gunter Leguy 0000-0002-9963-8076 9 Daniel Martin 0000-0003-4488-2538 10 Mathieu Morlighem 0000-0001-5219-1310 11 Frank Pattyn 0000-0003-4805-5636 12 David Pollard 13 Aurelien Quiquet 0000-0001-6207-3043 14 Christian Rodehacke 0000-0003-3110-3857 15 Helene Seroussi 0000-0001-9201-1644 16 Johannes Sutter 0000-0002-3357-2633 17 Tong Zhang 18 Jonas Van Breedam 0000-0003-1504-9520 19 Reinhard Calov 20 Robert DeConto 21 Christophe Dumas 22 Julius Garbe 0000-0003-3140-3307 23 G. Hilmar Gudmundsson 0000-0003-4236-5369 24 Matthew J. Hoffman 0000-0001-5076-0540 25 Angelika Humbert 0000-0002-0244-8760 26 Thomas Kleiner 0000-0001-7825-5765 27 William H. Lipscomb 28 Malte Meinshausen 0000-0003-4048-3521 29 Esmond Ng 30 Sophie M. J. Nowicki 0000-0001-6328-5590 31 Mauro Perego 32 Stephen F. Price 0000-0001-6878-2553 33 Fuyuki Saito 0000-0001-5935-9614 34 Nicole-Jeanne Schlegel 0000-0001-8035-448x 35 Sainan Sun 0000-0002-1614-2658 36 Roderik S. W. van de Wal 37 64530__28580__60ef6f94938c42b08075b8cb77f63cf4.pdf 64530.pdf 2023-09-19T12:28:30.2917690 Output 12524961 application/pdf Version of Record true © Author(s) 2020. Distributed under the terms of a Creative Commons Attribution 4.0 License (CC BY 4.0). false eng http://creativecommons.org/licenses/by/4.0/
title	Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
spellingShingle	Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2) Jim Jordan
title_short	Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
title_full	Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
title_fullStr	Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
title_full_unstemmed	Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
title_sort	Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
author_id_str_mv	6f28f48bfe39cb898ba51e3114889cbe
author_id_fullname_str_mv	6f28f48bfe39cb898ba51e3114889cbe_***_Jim Jordan
author	Jim Jordan
author2	Anders Levermann Ricarda Winkelmann Torsten Albrecht Heiko Goelzer Nicholas R. Golledge Ralf Greve Philippe Huybrechts Jim Jordan Gunter Leguy Daniel Martin Mathieu Morlighem Frank Pattyn David Pollard Aurelien Quiquet Christian Rodehacke Helene Seroussi Johannes Sutter Tong Zhang Jonas Van Breedam Reinhard Calov Robert DeConto Christophe Dumas Julius Garbe G. Hilmar Gudmundsson Matthew J. Hoffman Angelika Humbert Thomas Kleiner William H. Lipscomb Malte Meinshausen Esmond Ng Sophie M. J. Nowicki Mauro Perego Stephen F. Price Fuyuki Saito Nicole-Jeanne Schlegel Sainan Sun Roderik S. W. van de Wal
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container_title	Earth System Dynamics
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container_issue	1
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doi_str_mv	10.5194/esd-11-35-2020
publisher	Copernicus GmbH
college_str	Faculty of Science and Engineering
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department_str	School of Biosciences, Geography and Physics - Geography{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Biosciences, Geography and Physics - Geography
url	http://dx.doi.org/10.5194/esd-11-35-2020
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description	The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm. For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 ∘C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade.
published_date	2020-02-14T12:00:02Z
_version_	1778822364174221312
score	11.016235

Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)

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